MDS PREP
What is the function of the thick ascending limb of the loop of Henle?
1) Reabsorption of water
2) Secretion of hydrogen ions
3) Reabsorption of sodium, chloride, and bicarbonate
4) Reabsorption of urea
The thick ascending limb of the loop of Henle is responsible for the reabsorption of sodium, chloride, and bicarbonate, contributing to urine concentration.
An unstable membrane potential that will spontaneously depolarize is a property of which type of muscle?
1. Cardiac only
2. Cardiac and smooth
3. Skeletal and smooth
4. Skeletal and cardiac
Physiology
Answer: 1
The type of muscle that exhibits an unstable membrane potential that will
spontaneously depolarize is cardiac muscle.
Cardiac muscle cells, which are responsible for the contraction of the heart,
have an intrinsic ability to contract rhythmically without the need for external
stimulation. This is due to their unique property of automaticity, which is
mediated by the presence of the sinoatrial (SA) node and the subsequent
propagation of electrical impulses throughout the heart via the conduction
system. The SA node, often referred to as the "natural pacemaker" of the heart,
generates action potentials spontaneously and sets the heart rate.
The cardiac action potential involves a series of ionic currents across the cell
membrane that result in the depolarization and repolarization of the membrane.
During the resting phase, the membrane potential is maintained at a negative
value (around -90 mV) primarily due to the efflux of potassium ions (K+). When
the SA node initiates an action potential, voltage-gated sodium (Na+) channels
open, allowing an influx of sodium ions that leads to depolarization. Following
this, calcium (Ca2+) and more sodium ions enter the cell through voltage-gated
calcium (CaV) and sodium (Nav) channels, while potassium ions efflux through
various types of potassium (K+) channels, contributing to the plateau phase and
repolarization of the membrane.
The spontaneous depolarization of cardiac muscle cells is essential for the
coordinated contraction of the heart, which is critical for maintaining blood
circulation in the body. This property is not typically found in skeletal
muscles, which require an external signal from motor neurons to contract, nor in
smooth muscles, which are controlled by the autonomic nervous system and
hormones.
The reticular formation gives rise to which of the following extrapyramidal tracts?
1) Corticospinal tract
2) Reticulospinal tract
3) Vestibulospinal tract
4) Rubrospinal tract
E. Tectospinal tract
The reticulospinal tract arises from neurons in the reticular formation of the brainstem and projects to the spinal cord. It influences both voluntary and involuntary motor activities, modulating the excitability of motor neurons. The corticospinal tract arises from the cerebral cortex, the vestibulospinal tract from the vestibular nuclei, the rubrospinal tract from the red nucleus, and the tectospinal tract from the superior colliculus.
What is the role of the vagus nerve in the parasympathetic system?
1) Control of heart rate and gastric motility
2) Control of pupil dilation and salivation
3) Control of skeletal muscle contraction
4) Control of pituitary hormone secretion
The vagus nerve, as part of the parasympathetic system, innervates various organs in the thoracic and abdominal cavities, influencing heart rate and gastric motility among other functions.
What is the primary mechanism by which the stomach protects itself from self-digestion by its own enzymes?
1) Mucus secretion by gastric mucosal cells
2) Presence of intrinsic factor in the gastric juice
3) High concentration of bicarbonate in gastric juice
4) Low pH of gastric juice inhibiting its own enzymes
E) The mucosal lining is impermeable to H+ ions
The stomach protects itself from the harsh acidic environment and its own digestive enzymes through the secretion of a thick layer of mucus by mucosal cells. This mucus barrier forms a physical and chemical barrier that shields the underlying tissue from the acid and pepsin. Additionally, the stomach lining has a high turnover rate and is continuously regenerated, and the enzymes in the gastric juice are inactive until they come into contact with food.
The osmolarity of the tubular fluid in the medullary collecting duct is primarily controlled by which hormone?
1) Aldosterone
2) Atrial Natriuretic Peptide (ANP)
3) Antidiuretic Hormone (ADH)
4) Renin
The osmolarity of the tubular fluid in the medullary collecting duct is primarily controlled by Antidiuretic Hormone (ADH), which increases water reabsorption.
The increased venous return to the heart causes:
1. End diastolic volume increase
2. End systolic volume decrease
3. Decrease stroke volume
4. Decreased isovolumetric ventricular contraction.
Physiology
Answer: 1
The increased venous return to the heart causes End diastolic volume increase
In the somatosensory area-I of the cerebral cortex, which of the following statements is true?
1) The body is represented in a distorted manner, with the face and hands having a disproportionately larger representation than the rest of the body.
2) The body is represented in a manner proportional to its size, with no distortion in the representation of different body parts.
3) The body is represented in a reversed order, with the feet at the top and the face at the bottom of the postcentral gyrus.
4) Each side of the cortex receives sensory information from the same side of the body.
Answer: 1) The body is represented in a distorted manner in the somatosensory area-I, with the face and hands having a disproportionately larger representation due to their higher innervation density.